The practice of electrolysis upon aqueous solution results in production of water and an agglomerate. The latter can be separated from the water to produce a clean water. This process and its chemistry are well known, and many types of apparatus are used in the practice of it.
A primary problem in using an electrolytic process to produce clean water is a generally high cost of treatment. The direct cost of electricity is a significant part of the overall cost. The amount of electricity used in electrolytic processing is variable according to many factors in the design of an electrolytic reaction chamber. Design features that reduce electrical consumption are beneficial.
The cost of maintaining electrodes is another part of overall cost. Electrodes are consumed by the electrolytic reaction, but their consumption is basic to the chemistry of the reaction and is expected to occur over a predetermined time that is a function of reaction conditions. However, electrodes also can be fouled or short-circuited by deposit of reaction products. A fouled electrode becomes prematurely inefficient and can add to the amount of electricity consumed. Also, it will wear unevenly and will require premature replacement or removal for cleaning, either of which adds to maintenance cost and down-time for the reaction chamber. A reaction chamber that keeps its electrodes clean during electrolytic processing is beneficial.
A reaction chamber is designed to accommodate many aspects of the electrolytic process. Primarily, the chamber must be effective and efficient in its performance. Thus, such aspects as electrode composition, spacing, and surface area are considered. Sustainable spacing between electrodes is important, so that adjacent electrodes do not contact each other and thereby produce a short circuit. The flow path through the electrodes is a significant factor, as the length of the path influences the speed with which the reaction must be performed and, thus, influences the electrical requirements of the chamber. Ease of replacing electrodes is significant, both in terms of maintenance cost and the down-time of a reaction chamber. These are only a few of the considerations that influence design of reaction chamber, which is a complex process.
One desirable configuration for a reaction chambers is known as the “filter press” design. Electrode plates are interleaved with dielectric spacers and gaskets to form an electrode stack. The stack is capped at its opposite ends by end plates, which are clamped together by suitable bolts or the like. The bolts are tightened to clamp the end plates, in turn squeezing together the elements in the stack of electrodes, gaskets and spacers. The filter press design is desirable because the stack of electrode plates is a unit that is easy to handle. Further, the spacing between plates is well controlled. The end plates can be configured for connection to inlet and outlet conduits for feeding and removing a process liquid, and the electrode plates can be suitably apertured or otherwise configured to define a flow path between the electrodes in the stack. A filter press design lends itself to the use of electrode plates having a square or rectangular shape, which is easily fabricated and, therefore, relatively low in cost.
U.S. Pat. No. 1,541,947 to Hartman et al (1922) shows an early attempt at constructing such a filter press style reaction chamber. The electrodes are rectangular plates. Alternate plates are apertured near opposite narrower ends of the rectangle. Notably, two apertures are used at the perforated end of each rectangle. These apertures are transversely oblong, such that a considerable percentage of the perforated end is open for liquid flow from one processing chamber or zone to the next. Thus, the stack of electrodes defines a sinuous, longitudinal flow path from edge-to-edge of the rectangle, with the direction of flow reversing in each successive zone as the process liquid flows through the series of processing zones.
Later advances in chamber design reveal that edge-to-edge sinuous flow across a rectangle is not uniform. Fluid in certain areas between the electrodes will be stagnant, allowing precipitates to foul nearby surfaces of the electrodes. U.S. Pat. No. 4,124,480 to Stevenson discloses this problem in a filter-press design that employs edge-to-edge flow over rectangular plates in a stack. The electrode plates are slotted across the full width of alternating narrow ends to encourage the process liquid to flow over the full width of each electrode plate. However, even passing through a full width slot, the liquid stagnates along the edges of the plates, perhaps because of resistance induced by contact with the gasket or spacer located at such edges. Thus, it appears likely that longitudinal flow over a rectangular plate bounded by a side wall will be non-uniform and will result in fouling of certain areas of the plates.
The Stevenson patent also proposes a filter-press design using an alternate flow pattern with square electrode plates forming square treatment chambers. A first group of electrode plates are apertured at their center. A second group of electrode plates are relatively smaller in size than the first, such that they leave an almost continuous peripheral gap between each of the second group plates and the stack gaskets. In the second group, only the corners of the periphery are engaged between the gaskets and secure the second plates in the stack. The plates of the two groups are arranged in the stack in alternating sequence. The resulting flow path is from the center of a plate in the first group to the periphery of a plate in the second group, and vice versa.
However, it can be readily seen that such center-to-periphery and periphery-to-center flow will be non-uniform when square treatment chambers are used. In a stack of square plates, the shortest flow path, and likely the one with least resistance, is between the center hole of one plate and the midpoint along any of the four edges of a juxtaposed plate. Fouling is likely along the relatively longer flow paths near the corners of all plates in the stack, with resulting uneven wear, poorly predictable process control, higher electricity usage, short circuits, and premature plate replacement or maintenance.
It is evident that circular plates would be no more successful in producing equal length radial flow paths. Fabricating and assembling a stack of circular plates is likely to be more expensive and will not solve the problems of premature fouling. Like square plates, circular plates must be configured with portions that engage the stack gaskets; and they must provide apertures or peripheral gaps that establish a sinuous flow path between plates. A circular shape is little better than a square one in meeting these two requirements. Uneven flow paths or stagnant areas are inevitable results. Circular plates are likely to behave similarly to square plates in suffering prematurely fouled areas.
It would be desirable to overcome the existing fouling problems in reaction chambers of the filter-press design. In particular, it would be desirable to have a chamber design producing predictable wear patterns in which fouling is not a substantial issue. Such a design would enable the reaction chamber to be operated with sustained process efficiency over a predictable interval. Such a predictable interval can be determined by calculating the consumption of the electrodes according to the reaction parameters imposed upon the chamber, rather than by the unpredictable time between loss of efficiency due to fouling. Maintenance or replacement operations can be performed at scheduled intervals, allowing a high degree of confidence that the electrocoagulation process will remain effective and efficient between such service.
Further, it would be desirable to construct an electrocoagulation chamber in such a way that assembly and disassembly required very little time or technical skill. Thus, a chamber should allow streamlined insertion and removal of electrode plates or blades, as well as of spacers.
To achieve the foregoing and other objects and in accordance with the purpose of the present invention, as embodied and broadly described herein, the electrocoagulation chamber and method of this invention may comprise the following.